That's a pair of Genasun LFP Lithium batteries that weigh a small fraction of what similar sized regular marine batteries would and offer a lot more usable power than even their 760 amp hour rating would indicate, because they can endure truly deep discharges and accept massive recharges.  Combine these with no less than four Victron MultiPlus inverter/chargers, which can automatically kick in extra AC when shore power or the generator can't carry the load, and you've got power to spare.  Yes, this is a high end project, but note the gray diagonal planking seen behind the lithium batteries...